River herring (alewife Alosa pseudoharengus and blueback herring Alosa aestivalis) have historically supported valuable fisheries along the Atlantic Coast and served as important components of coastal ecosystems.They are anadromous fish which live much of their lives in the ocean but migrate to freshwater to spawn in the same streams where they were born. Over the past several decades, however, river herring numbers have declined significantly, leading to closures of fisheries including those in Chesapeake Bay.

Funded by the National Fish and Wildlife Foundation and the Smithsonian Institution, the project has a long-term goal of documenting and monitoring river herring spawning runs throughout Chesapeake Bay. This will be accomplished using a variety of methods from simple visual assessments of the presence or absence of spawning fish in individual streams to run counts made using cutting-edge technology.

A major focus of our current work is using Dual-frequency Identification Sonar (DIDSON), also known as imaging sonar, to track the river herring spawning runs in parts of the Nanticoke and Choptank Rivers. This cutting-edge technology allows us to record and count adult fish as they swim past a sonar station during their spawning runs, which occur in spring. Imaging sonar allows us to overcome challenges to counting fish in tributaries of Chesapeake Bay such as turbid water, which prevents visual counts, and problems with obtaining accurate counts of schooling fish from net-based sampling methods. It also allows us to sample throughout the day and night without having to be present on site.

After the DIDSON has been deployed and footage collected, the footage is reviewed and analyzed back at the lab to generate fish counts and size estimates. Species identifications are made by conducting additional sampling each week of the spawning run using electrofishing (top photo).

We are also using DIDSON to verify the accuracy of other, lower-cost methods of estimating the size of river herring runs. These other methods include electrofishing and tracking of ichthyoplankton (herring eggs and larvae) abundance (photo at right). By exploring different methods of determining the size of spawning runs, we will be able to design a cost-effective combination of both highly accurate and less accurate but inexpensive methods of monitoring river herring runs throughout Chesapeake Bay.

Our work on river herring will help contribute to conservation of this important species, which is currently a Candidate Species under consideration for listing as Threatened under the Endangered Species Act.